Small pore size nonwoven mat with hydrophilic/acid resistant filler used in lead acid batteries and applications therefor

ABSTRACT

According to one embodiment, a nonwoven fiber mat includes between 10% and 50% by weight of a plurality of first glass fibers having an average diameter of less than 5 μm and between 50% and 90% by weight of a plurality of second glass fibers having an average diameter of greater than 6 μm. The nonwoven fiber mat also includes an acid resistant binder that binds the first and second glass fibers together. The nonwoven fiber mat has an average pore size of between 1 and 100 μm and exhibits an air permeability of below 100 cubic feet per minute per square foot (cfm/ft 2 ) as measured by the Frazier test at 125 Pa according to ASTM Standard Method D737.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of pending U.S. application Ser. No.14/642,361, filed Mar. 9, 2015.

This application is related to U.S. application Ser. No. 14/642,273,entitled “WICKING NONWOVEN MAT FORM WET-LAID PROCESS,” to Guo et al.filed on Mar. 9, 2015, now U.S. Pat. No. 9,716,293 issued Jul. 5, 2017,the entire contents of which are incorporated by reference herein.

BACKGROUND

Electrodes or electrode plates commonly used in lead-acid batteriesoften include a metallic grid that is used to support lead and/or leadoxide pastes. During charge and discharge cycles, the volume of the leadand/or lead oxide paste typically expands and contracts. Repeated usageand, thus, repeated charge and discharge cycles may have negativeeffects on the electrode, such as shedding of the active materialparticles of the lead and/or lead oxide pastes. To reduce those negativeeffects, the electrodes may be reinforced with pasting media or pastingpaper to keep the lead or lead oxide paste intact. These pasting papersalso may have the advantage of wicking electrolyte along the electrodeplates. This wicking may help battery performance. These pasting papersin the battery should have adequate wickability and tensile strength,including in the harsh chemical environment within the battery. Theseand other characteristics and improvements of pasting papers areaddressed.

BRIEF SUMMARY

In some instances it may be desired to reduce the air permeabilityand/or pore size of a nonwoven mat that is used to reinforce anelectrode of a lead-acid battery. Such mats may exhibit improvedfunction in limiting shedding of the electrode's active material, whichmay enhance the life and performance of the battery. According to oneaspect, a lead-acid battery is provided. The lead-acid battery includesa positive electrode, a negative electrode, and a nonwoven fiberreinforcement mat that is disposed adjacent the positive electrode orthe negative electrode. The nonwoven fiber reinforcement mat includes aplurality of first glass fibers having an average fiber diameter of lessthan 5 μm (more commonly less than 3 μm), a plurality of second glassfibers having an average fiber diameter of greater than 6 μm (morecommonly between 10 μm and 15 μm), and an acid resistant bindercomposition that binds the plurality of first glass fibers and secondglass fibers together. The nonwoven fiber reinforcement mat includesbetween about 10% and about 50% by weight of the plurality of firstglass fibers and between about 50% and 90% by weight of the plurality ofsecond glass fibers. The nonwoven fiber reinforcement mat has an averagepore size of between 1 μm and 100 μm and exhibits an air permeability ofbelow 100 cubic feet per minute per square foot (cfm/ft²) as measured bythe Frazier test at 125 Pa according to ASTM Standard Method D737. Insome embodiments, the nonwoven fiber reinforcement mat has an averagepore size of between 1 and 10 μm and/or exhibits an air permeability ofbelow 10 cfm/ft² or even 1 cfm/ft² as measured by the Frazier test at125 Pa according to ASTM Standard Method D737.

According to another aspect, a nonwoven fiber reinforcement mat that isconfigured for reinforcing an electrode of a lead-acid battery isprovided. The nonwoven fiber reinforcement mat includes a plurality offirst glass fibers having an average diameter of less than 5 μm (morecommonly less than 3 μm), a plurality of second glass fibers having anaverage diameter of greater than 6 μm (more commonly between 10 μm and15 μm), and an acid resistant binder composition that binds theplurality of first glass fibers and second glass fibers together. Thenonwoven fiber reinforcement mat includes between about 10% and about50% by weight of the plurality of first glass fibers and between about50% and 90% by weight of the plurality of second glass fibers. Thenonwoven fiber reinforcement mat has an average pore size of between 1μm and 100 μm and exhibits an air permeability of below 100 cubic feetper minute per square foot (cfm/ft²) as measured by the Frazier test at125 Pa according to ASTM Standard Method D737. In some embodiments, thenonwoven fiber reinforcement mat has an average pore size of between 1and 10 μm and/or exhibits an air permeability of below 10 cfm/ft² oreven 1 cfm/ft² as measured by the Frazier test at 125 Pa according toASTM Standard Method D737.

According to yet another aspect, a method of making a nonwoven fiber matfor use in reinforcing an electrode of a lead-acid battery is provided.The method includes mixing a plurality of first glass fibers with aplurality of second glass fibers in a white water solution where thefirst glass fibers have an average fiber diameter of less than 5 μm andthe second glass fibers have an average fiber diameter of greater than 6μm. The method also includes removing a liquid of the white watersolution to form a wet laid mat comprising about 10% and about 50% byweight of the plurality of first glass fibers and between about 50% and90% by weight of the plurality of second glass fibers. The methodfurther includes adding a binder composition to the wet laid mat anddrying the wet laid mat and binder composition to produce the nonwovenfiber mat. The nonwoven fiber mat has an average pore size of between 1μm and 100 μm and exhibits an air permeability of below 100 cubic feetper minute per square foot (cfm/ft²) as measured by the Frazier test at125 Pa according to ASTM Standard Method D737.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technology is described in conjunction with the appendedfigures:

FIG. 1 illustrates an exploded perspective view of a battery cellassembly;

FIG. 2 illustrates an assembled cross section view of the battery cellassembly of FIG. 1;

FIGS. 3A-3C illustrate cross section views of various configurations ofan electrode or plate and a nonwoven fiber mat;

FIG. 4 illustrates a process for preparing an electrode or plate havinga nonwoven fiber mat disposed on or near a surface of the electrode orplate;

FIG. 5 illustrates a block diagram of a method of making a nonwovenfiber mat for reinforcing an electrode of a lead-acid battery orsupporting a separator of a lead-acid battery; and

FIG. 6 shows a block diagram of a method of making a nonwoven fiber mat.

DETAILED DESCRIPTION

Conventional methods of producing nonwoven fiber mats or pasting papersmay result in a fiber mat or pasting paper that is structurally weakand/or suffers from other issues. For example, conventional methodstypically produce mats or paper for AGM batteries that are composedessentially of 100% glass microfibers and that are thin, very closed-up,and soft. These mats or paper are typically weak, but exhibit goodwicking properties. The nonwoven fiber mat may have high wickingproperties, above what is needed for lead-acid batteries and otherapplications. A wickable nonwoven fiber mat in a battery may helpmaintain electrolyte or other liquid coverage of electrode plates, butlittle, if any, data exists to support the high level of wickability inconventional nonwoven fiber mats. This overdesigned wickabilitycharacteristic may be the result of a higher concentration ofmicrofibers relative to coarse fibers. An increased concentration ofmicrofibers compared to coarse fibers may result in a nonwoven fiber matwith decreased mechanical strength, which may result from the lowerindividual mechanical strength with smaller diameter fibers. Pasting mator paper for flooded lead-acid batteries that are produced viaconventional methods are typically very open and thin and do not exhibitgood wicking properties. These mats are commonly stronger than thoseproduced for AGM batteries.

Additionally, in addition to providing wickability, in many applicationsthe pasting paper is used to support the active material to limit orprevent shedding of the active material from the electrode. Thestructural support and/or wickability that the pasting paper providesmay be enhanced by reducing the porosity and/or air permeability of thepasting paper. As described in greater detail blow, the porosity and/orair permeability of the pasting paper may be decreased by using fillermaterials and/or increasing the amount of microfibers that are used inthe pasting paper. Conventional pasting papers for flooded lead acidbatteries typically do not reduce the porosity and/or air permeabilityof the pasting paper due to the increase in electrical resistance thatresults for a decreased porosity and/or air permeability of the pastingpaper. Conventional pasting papers for AGM batteries typically exhibitlow porosity and air perm. Unlike flooded lead acid batteries, theresistance for AGM pasting papers is not an issue because the pastingpapers exhibit good wicking properties. For convenience in describingthe embodiments herein, the application will focus mainly on the use ofthe embodiments in flooded lead acid batteries. It should be realized,however, that the embodiments described herein may also be used in AGMbattery applications. In such embodiments, the nonwoven fiber mat willgenerally comprise a majority of smaller diameter fibers, such asmicrofibers.

Conventional processes of making nonwoven fiber mats for AGM batteriesand other applications may be more expensive and/or have lowerthroughput. The higher concentration of microfibers, which are generallymore expensive than coarse fibers, may increase material cost. Acids mayoften be used to disperse microfibers to create a uniform mixture ofmicrofibers and coarse fibers. The low pHs (usually less than 3) may becorrosive, and the process may require equipment made from stainlesssteel or other expensive materials. Because of the challenge indispersing microfibers, conventional processes may be run in batch orsemi-batch operations to ensure a sufficiently uniform mixture offibers. For these and other reasons, materials and methods used inconventional nonwoven fiber mat for AGM battery technologies may not becost effective or efficient.

In many embodiment, the nonwoven fiber mats consist of coarse glassfibers and glass micro-fibers that are homogeneously dispersedthroughout the nonwoven fiber mat. This configuration or composition isdifferent than that employed for conventional mats, which typically havea dual layer construction—i.e., coarse fibers forming a layer andmicrofibers forming another layer adjacent the layer of coarse fibers.For example, U.S. Pat. No. 4,336,314 to Yonezu et al., describes aconventional mat having such a duel layered construction. Conventionalmats employ the dual layer construction due to the difficulty inhomogeneously dispersing coarse glass fibers and micro-glass fibersduring formation of the nonwoven fiber mat. For example, as known in theart, producing a nonwoven glass mat having coarse glass fibers in a wetlaid process requires a set of parameters that are vastly different thanthe parameters that are used to produce a nonwoven glass mat havingmicro-fibers. The vast difference in the manufacturing parameterstypically results in a concentration of one of the fibers within theresulting nonwoven fiber mat. In contrast, the manufacturing processused to produce the nonwoven fibers mats described herein are highlycontrolled and optimized to produce a homogenous dispersion of thecoarse glass fibers and micro-glass fibers in the resulting nonwovenfiber mat. The resulting homogenous nonwoven fiber mat exhibits manybenefits over the dual layered construction of conventional mats. Forexample, the homogenous nonwoven fiber mat exhibits a relatively uniformresistance across the mat, which results in a uniform current and/orutilization of the active materials.

As used herein the term “pasting paper” refers to a material that isplaced adjacent an electrode of a lead acid battery, typically duringthe manufacture of the electrode such as during the application of theactive material to a metal grid. The pasting paper may remain in placeadjacent the electrode during use of the lead acid battery to limit orprevent shedding of the active material from the electrode. Although theterm “paper” is used in describing the material, in many of theembodiments described herein the pasting paper material is a nonwovenfiber mat that is typically made of a combination of glass fibers. Insome embodiments the nonwoven fiber mat may consist entirely of glassfibers, although in other embodiments various other fiber types may alsobe used including polymeric fibers, cellulose fibers, and the like. Theterm pasting paper may be used interchangeably herein with reinforcementmat, nonwoven fiber reinforcement mat, and/or nonwoven fiber mat, but itshould be realized that these terms may refer to the same material.Other filler materials may also be added to the nonwoven fiber mat forvarious reasons, some of which are described in greater detail herein.These and other aspects of the embodiments may be more fully appreciatedwith reference to the description of the several figures provided hereinbelow.

FIGS. 1 and 2, respectively, show a perspective exploded view of alead-acid battery cell 200 and a cross-section assembled view of thelead-acid battery cell 200. The lead-acid battery cell 200 may representa cell used in either flooded lead-acid batteries or Absorptive GlassMat (AGM) batteries. Each cell 200 may provide an electromotive force(emf) of about 2.1 volts and a lead-acid battery may include 3 suchcells 200 connected in series to provide an emf of about 6.3 volts ormay include 6 such cells 200 connected in series to provide an emf ofabout 12.6 volts, and the like. Cell 200 may include a positive plate orelectrode 202 and a negative plate or electrode 212 separated by batteryseparator 220 so as to electrically insulate the electrodes 202 and 212.Positive electrode 202 may include a grid or conductor 206 of lead alloymaterial. A positive active material 204, such as lead dioxide, istypically coated or pasted on grid 206. Grid 206 is also typicallyelectrically coupled with a positive terminal 208. Grid 206 providesstructural support for the positive active material 204 along withelectrical conductivity to terminal 208.

Likewise, negative electrode 212 includes a grid or conductor 216 oflead alloy material that is coated or pasted with a negative activematerial 214, such as lead. Grid 216 is electrically coupled with anegative terminal 218. Like grid 206, grid 216 structurally supports thenegative active material 214 along with providing electrical conductanceto terminal 218. In flooded type lead-acid batteries, positive electrode202 and negative electrode 212 may be immersed in an electrolyte (notshown) that may include a sulfuric acid and water solution. In AGM typelead-acid batteries, the electrolyte may be absorbed and maintainedwithin battery separator 220. Battery separator 220 may be positionedbetween positive electrode 202 and negative electrode 212 to physicallyseparate and electrically insulate the two electrodes while enablingionic transport, thus completing a circuit and allowing an electroniccurrent to flow between positive terminal 208 and negative terminal 218.Separator 220 may include a microporous membrane (i.e., the solid blackcomponent), which is often a polymeric film having negligibleconductance. The polymeric film may include micro-sized voids that allowionic transport (i.e., transport of ionic charge carriers) acrossseparator 220. In some examples, the microporous membrane or polymericfilm may have a thickness of 50 micrometers or less, including 25micrometers or less, may have a porosity of about 50% or 40% or less,and may have an average pore size of 5 micrometers or less, including 1μm or less. The polymeric film may include various types of polymersincluding polyolefins, polyvinylidene fluoride, polytetrafluoroethylene,polyamide, polyvinyl alcohol, polyester, polyvinyl chloride, nylon,polyethylene terephthalate, and the like. Separator 220 may also includeone or more fiber mats (e.g., separator support mat) that are positionedadjacent one or both sides of the microporous membrane/polymeric film toreinforce the microporous membrane and/or provide puncture resistance.In AGM applications, the polymeric film may not be included. Instead,the nonwoven fiber mat separator 220 may be relatively thick and used toboth absorb the electrolyte and electrically isolate the positive andnegative electrodes.

Positioned near a surface of negative electrode 212 may be a nonwovenfiber mat 230 (referred to herein as a reinforcement mat, nonwoven fiberreinforcement mat, or nonwoven fiber mat). Reinforcement mat 230 may bedisposed partially or fully over the surface of negative electrode 212so as to partially or fully cover the surface. As shown in FIG. 3A-C, areinforcement mat 230 may be disposed on both surfaces of the negativeelectrode 212, or may fully envelope or surround the electrode.Likewise, although reinforcement mat 230 is shown on the outer surfaceof the electrode 212, in some examples, reinforcement mat 230 may bepositioned on the inner surface of the electrode 212 (i.e., adjacentseparator 220). Reinforcement mat 230 may reinforce the negativeelectrode 212 and may provide an additional supporting component for thenegative active material 214. The additional support provided byreinforcement mat 230 may help reduce the negative effects of sheddingof the negative active material particles as the active material layersoftens from repeated charge and discharge cycles. This may reduce thedegradation commonly experienced by repeated usage of lead-acidbatteries. As described in greater detail below, the structural supportprovided by the reinforcement mat 230 may be greatly enhanced byreducing the porosity and/or air permeability of the reinforcement mat230.

Reinforcement mat 230 may often be impregnated or saturated with thenegative active material 214 so that the reinforcement mat 230 ispartially or fully disposed within the active material 214 layer.Impregnation or saturation of the active material within thereinforcement mat means that the active material penetrates at leastpartially into the mat. For example, reinforcement mat 230 may be fullyimpregnated with the negative active material 214 so that reinforcementmat 230 is fully buried within the negative active material 214 (i.e.,fully buried within the lead paste). Fully burying the reinforcement mat230 within the negative active material 214 means that the mat isentirely disposed within the negative active material 214. For example,reinforcement mat 230 may be disposed within the negative activematerial 214 up to about a depth X of about 20 mils (i.e., 0.020 inches)from an outer surface of the electrode 212. In other examples, the glassmat 230 may rest atop the negative active material 214 so that the matis impregnated with very little active material. Often the reinforcementmat 230 may be impregnated with the negative active material 214 so thatthe outer surface of the mat forms or is substantially adjacent theouter surface of the electrode 212 (see reinforcement mat 240). In otherwords, the active material may fully penetrate through the reinforcementmat 230 so that the outer surface of the electrode 212 is a blend ormesh of active material and reinforcement mat fibers.

The thickness of the glass mat may be a function of mat weight, bindercontent (as measured by Loss on Ignition [LOI]), and fiber diameter. Thetype of binder used and the length of the fibers may be weaker factorsin determining the glass mat thickness. Higher binder content, however,may generally reduce the glass mat thickness, although excessive binderuse may pose various processing challenges during mat production andthereafter. A lower mat weight may also reduce the mat thickness. Themat weight, however, may also be limited because the mat needs toprovide enough tensile strength during winding and downstream processes.

As described herein, reinforcement mat 230 may include a plurality ofglass fibers and an acid resistant binder that couples the plurality ofglass fibers together to form the reinforcement mat. Reinforcement mat230 may have an area weight of between about 10 and 100 g/m², includingbetween about 20 and 60 g/m². Reinforcement mat 230 may be used forreinforcing a plate or electrode of a lead-acid battery and may includea relatively homogenous mixture of coarse glass fibers that may includea plurality of first glass fibers having a diameter between about 0.01-5μm and a plurality of second fibers having a diameter of at least 6 μm.In some examples the relatively homogenous mixture may make up betweenabout 70-95% of the mass of the mat 230. In some examples, thehomogenous mixture may also include 5-30% conductive fibers. Forexample, conductive fibers having diameters about 6 μm and above andhaving lengths between about 8 and 10 mm can be included in therelatively homogenous mixture. The reinforcement mat 230 also includesan acid resistant binder that bonds the plurality of first and secondglass fibers together to form the reinforcement mat 230. Thereinforcement mat 230 further includes a wetting component that isapplied to reinforcement mat 230 to increase the wettability/wickabilityof the reinforcement mat 230. The wettability/wickability of thereinforcement mat 230 may be increased such that the reinforcement mat230 has or exhibits an average wick height of 40 wt. % sulfuric acid ofat least 1.0 cm after exposure to the respective solution for 10 minutesin accordance with a test conducted according to method ISO8787.

As briefly described above, reinforcement mat 230 may include aplurality of electrically insulative fibers, such as glass, polyolefin,polyester, and the like, which are primarily used to reinforce theelectrode. Because the reinforcement mat 230 may be made of suchinsulative fibers, the reinforcement mat 230 may be essentiallynon-conductive prior to or without the addition of the conductivematerial. For example, without combining or adding the conductivematerial/layer, the reinforcement mat 230 may have an electricalresistance greater than about 1 Megohm per square. In manufacturing thereinforcement mat 230, water or another liquid may be removed (e.g., viaa vacuum) from a suspension of the fibers in the liquid medium. A bindermay then be applied to the wet-laid non-woven glass or polyolefin fibersto form reinforcement mat 230. As described previously, in someexamples, the conductive material or fibers may be added to the binderand/or to the liquid medium. As an example, reinforcement mat 230 mayhave a thickness of between about 50 μm and about 500 μm and have anaverage pore size of between about 5 μm and about 5 millimeters.

The reinforcement mat 230 also may include a wetting component that isapplied to the reinforcement mat to increase the wettability/wickabilityof the reinforcement mat. The wettability/wickability of thereinforcement mat 230 may be increased so that the reinforcement mat hasor exhibits an average wick height of 40 wt. % sulfuric acid of at least0.5 cm after exposure to the respective solution for 10 minutes inaccordance with a test conducted according to method ISO8787. The matmay exhibit an average wick height of the 40 wt. % sulfuric acidsolution of at least 0.5 cm without an additional wetting component.

As described herein, the wetting component may be a wettable componentof the acid resistant binder (e.g., a hydrophilic functional group), ahydrophilic binder that is mixed with the acid resistant binder, thewetting component may be component fibers (e.g., cellulose, cotton,other natural fibers, polyester, other synthetic fibers, or acombination of natural and/or synthetic fibers) that are bonded with theglass fibers of the reinforcement mat 230, or the wetting component maybe a wettable solution (e.g., starch or cellulose solution) that isapplied to the reinforcement mat 230 such that the wettable solutionsaturates the reinforcement mat 230 or is disposed on at least onesurface of the reinforcement mat 230 upon drying of the wettablesolution. In some examples, the wetting component may include acombination of any of the aforementioned components, such as acombination of cellulose fibers and an acid resistant binder having awettable component. In specific examples, the glass fibers ofreinforcement mat 230 may include first fibers having fiber diametersbetween about 0.5 μm and about 5 μm or between about 0.5 μm and about 1μm and second fibers having fiber diameters of at least about 6 μm.According to some examples, the component fibers may form a componentfiber mat that is bonded to at least one side of the glass reinforcementmat 230 such that the reinforcement mat 230 comprises a two layer matconfiguration. The component fibers may be mixed with the glass fiberssuch that upon forming the glass mat the component fibers may beentangled with and bonded to the glass fibers.

Referring now to FIGS. 3A-3C, illustrated are variouselectrode-reinforcement mat configurations. FIG. 3A illustrates aconfiguration where an electrode 300 has a single reinforcement mat 302disposed on or near an outer surface. As described above, reinforcementmat 302 may include a conductive material and/or layer so as to enableelectron flow on a surface and/or through reinforcement mat 302 to abattery terminal. Reinforcement mat 302 may also include a wettingcomponent as described above to provide the mat 302 with enhancedwettability characteristics. Reinforcement mat 302 may partially orfully cover the outer surface of electrode 300. The configuration ofFIG. 3B may be similar to that of FIG. 3A except that an additionalreinforcement mat 304 may be disposed on or near an opposite surface ofelectrode 300 so that electrode 300 may be sandwiched between the twoglass mats, 302 and 304. Either or both reinforcement mats, 302 and 304,may include a conductive material and/or layer to enable electron flowto a battery terminal as well as a wetting component. As such, electrode300 may be sandwiched between two conductive reinforcement mats 302 and304. FIG. 3C illustrates a configuration where a reinforcement mat 306may envelop or surround electrode 300. Although FIG. 3C illustrates thereinforcement mat 306 fully enveloping the electrode 300, in manyexamples a top side or portion of the mat 306, or a portion thereof, isopen. Glass mat 306 may include the conductive material and/or layer asdescribed above to enable electron flow as well as a wetting component.

Referring back to FIGS. 1 and 2, positioned near a surface of positiveelectrode 202 is a reinforcement mat 240. Reinforcement mat 240 may bearranged and/or coupled with positive electrode 202 similar to thearrangement and coupling of reinforcement mat 230 with respect tonegative electrode 212. For example, reinforcement mat 240 may bedisposed partially or fully over the surface of positive electrode 202so as to partially or fully cover the surface, may be positioned on aninner surface of the electrode 202 (i.e., adjacent separator 220)instead of the shown outer surface configuration, and/or may beimpregnated or saturated with the positive active material 204 so thatthe reinforcement mat 240 is partially or fully disposed within theactive material 204 layer. Like reinforcement mat 230, reinforcement mat240 may provide additional support to help reduce the negative effectsof shedding of the positive active material particles due to repeatedcharge and discharge cycles.

With regard to the reinforcement functions of reinforcement mats 230and/or 240, in some examples the reinforcing aspects of these mats maybe enhanced by blending fibers having different fiber diameters.Reinforcement mats 230 and 240 (referred to hereinafter as reinforcementmat 230) can have similar characteristics and compositions, and caninclude a blend of two or more different diameter fibers. Reinforcementmat 230 includes a plurality of first microfibers, having fiberdiameters ranging between about 0.5 μm and about 5 μm, between about 0.5μm and about 1 μm, or between about 0.7 μm and about 2 μm. The firstmicrofibers are blended with a plurality of second coarse fibers, havingfiber diameters of at least about 6 μm, and typically between about 8 μmand about 20 μm, and more commonly between about 10 μm and about 15 μm.In some examples, the plurality of second coarse fibers may include asilane material sizing. The blend of the two or more different diameterfibers results in a mat that is sufficiently strong to structurallysupport the active material as described above and to withstand thevarious plate manufacturing processes while also minimizing thethickness and overall size of the mat. Reducing the thickness ofreinforcement mat 230 while maintaining mat strength may be desiredsince reinforcement mat 230 typically is a chemically inactive componentand, thus, does not contribute to the battery's electrochemical process.Reducing the volume of reinforcement mat 230 helps minimize thebattery's volume of non-electrochemically contributing components.

In examples, reinforcement mat 230 includes a blend of between 10% and50% of the first microfibers and between 50% and 90% of the secondcoarse fibers. In these or other examples, reinforcement mat 230 mayinclude a blend of between 20% and 30% of the first microfibers andbetween 70% and 80% of the second coarse fibers. In these or otherexamples, reinforcement mat 230 may include a blend of between 30% and50% of the first microfibers and between 50% and 70% of the secondcoarse fibers. In some examples, reinforcement mat 230 may include ablend of between 15% and 40% of the first microfibers and between 60%and 85% of the second coarse fibers. In yet other examples, the blend offirst microfibers and second coarse fibers is approximately equal (i.e.,50% of the first microfibers and second coarse fibers).

The length of the coarse fibers may also contribute to the overallstrength of reinforcement mat 230 by physically entangling with adjacentfibers or fiber bundles and/or creating additional contact points whereseparate fibers are bonded via an applied binder. In examples, thecoarse fibers have fiber lengths that range between about ⅓ inch andabout 1½ inches, although an upper length limit of 1¼ inch is morecommon. This range of lengths provides sufficient mat strength whileallowing the fibers to be dispersed in a white water solution for matprocessing applications. In other examples, the coarse fibers have fiberlengths that range between ½ and ¾ of an inch. The fibers lengths of thefirst microfibers may be different than the fibers lengths of the secondcoarse fibers.

The type and amount of binder used to bond the first microfiber andsecond coarse fibers together may also contribute to the overallstrength and thickness of reinforcement mat 230. As described above, thebinder is generally an acid and/or chemically-resistant binder thatdelivers the durability to survive in the acid environment throughoutthe life of the battery, the strength to survive the plate pastingoperation, and the permeability to enable paste penetration. Forexample, the binder may be an acrylic binder, a melamine binder, a UFbinder, or the like. The binder may also include and bond the conductivematerial to the first and/or second coarse fibers. Increased binderusage may reduce the thickness of reinforcement mat 230 by creating morefiber bonds and densifying reinforcement mat 230. The increased fibersbonds may also strengthen reinforcement mat 230. In examples, the binderis applied to the first microfibers and second coarse fibers such thatthe binder comprises between about 5% and 45% by weight of thereinforcement mat 230 or between about 15% and 35% by weight of thereinforcement mat. In some examples, the binder is applied to the firstmicrofibers and second coarse fibers such that it comprises betweenabout 5% and 30% by weight of the reinforcement mat 230.

As described herein, the conductive material may be mixed with thebinder or a secondary binder and applied to the first and/or secondcoarse fibers during manufacture of the reinforcement mat 230 orsubsequent thereto.

The wetting component may be mixed with the binder in some examples. Theresulting reinforcement mat 230 may have or exhibit an average wickheight of at least 0.5 cm after exposure to sulfuric acid having 40 wt.% H2SO4 and/or a specific gravity of 1.28 for 10 minutes conductedaccording to method ISO8787, except that sulfuric acid having 40 wt. %H2SO4 and/or a specific gravity of 1.28 is used in place of water. Thewetting component may be dissolvable in an acid solution of thelead-acid battery such that a significant portion of the nonwoven fibermat is lost due to dissolving of the wetting component. For example,between about 5-85% of the mass of the reinforcement mat 230 may belost.

Referring now to FIG. 4, illustrated is a process 400 for manufacturingan electrode. The process may involve transporting a lead alloy grid 410on a conveyor toward an active material 430 applicator (e.g., lead orlead oxide paste applicator), which applies or pastes the activematerial 430 to the grid 410. A nonwoven mat roll 420 may be positionedbelow grid 410 so that a reinforcement mat is applied to a bottomsurface of the grid 410. The reinforcement mat may include a conductivematerial and/or layer, as well as a wetting component, as describedherein. In some examples, the reinforcement mat may also include a blendof fibers as described herein. In some examples, the reinforcement matmay also include a blend of coarse fibers and microfibers in addition tothe wetting component as described herein. A second nonwoven mat roll440 may be positioned above grid 410 so that a second reinforcement matis applied to a top surface of the grid 410. The second reinforcementmat may also include a conductive material, a wetting component, and/orlayer and/or blend of coarse fibers and/or microfibers (similar to ordifferent from reinforcement mat 420). The resulting electrode or plate450 may subsequently be cut to length via a plate cutter (not shown). Asdescribed herein, the active material 430 may be applied to the grid 410and/or top and bottom of reinforcement mats, 440 and 420, so that theactive material impregnates or saturates the mats to a desired degree.The electrode or plate 450 may then be dried via a dryer (not shown) orother component of process 400. As described herein, the reinforcementmats, 440 and 420, may aid in the drying of the electrode or plate 450by wicking the water and/or water/acid solution from the electrode orplate 450 so as to allow the water and/or water/acid solution toevaporate.

As described briefly above, one of the main functions of the pastingpaper is to minimize the shedding of active materials during chargingand discharging of the battery. The reduced shedding of the activematerials is believed to prolong the life of the battery. Activeshedding is reduced by the structural support provided by the pastingpaper. When the active material is shed, it may not participate in thechemical reaction that produces battery power. For example, when theactive material is shed from the plate, it may mix with or into theelectrolyte. The active material may sink to the bottom of the batteryif the active material particles are sufficiently large. This shedactive material cannot reform with the plate and therefore cannot beused in the chemical reaction. In other words, the shed material is notan “active material” any longer. As such, the utilization of activematerial is reduced, which negatively effects the battery performanceand life. Similarly, when the shed active material particle size issmall, the shed active material from the positive plate can leak ormigrate to the negative side to convert to lead. The lead particles canalign and shorten the positive and negative plates. The wickabilityand/or structural support provided by the pasting paper may be increasedby reducing the porosity and/or air permeability of the pasting paper.The porosity and/or air permeability of the pasting paper may bedecreased by using filler materials and/or increasing the amount ofmicrofibers that are used in the pasting paper.

In regards to the wickability of conventional mats, conventionalprocesses typically use a thin nonwoven glass mat or PET (polyethyleneterephthalate) mat for the plate pasting applications in flooded leadacid batteries. PET mats are commonly used for “EFB” batteries (EnhancedFlooded Battery). In general, these mats do not have any significantwicking property—i.e., the wicking height is essentially zero by thetest method defined in 1S08787. A mat with good wicking properties isdesirable because it tends to reduce the internal resistance of thebattery. As described above, some AGM batteries use mats that areessentially made of glass microfibers. However, these mats are likelyover engineered for the wicking purposes and lack sufficient strength,which can cause processing issues during pasting and therefore lowerefficiency of the battery. A mat possessing good wicking and strengthproperties is desired.

In regards to separators, the configuration of a polyethylene membranewith a supporting mat (typically a nonwoven glass mat withoutsignificant wicking property) does not work well when routine batterymaintenance is not performed (e.g., fail to add water regularly) or whenthe battery is under high temperatures for a prolonged period of time.The battery tends to lose water (partial “dry out”), which leads to atleast two issues. First, the upper parts of the electrode plates areexposed to air and the negative plates can be oxidized. In addition, dueto less volume of the electrodes in the electrolyte, the usage of activematerials can be reduced, therefore lowering the capacity andperformances of the battery. Second, the electrolyte sulfuric acidbecomes more concentrated and the resulting acid concentration is notoptimal. This higher concentration may reduce the battery performancesas well as be more corrosive to all the battery parts, include theplates, separator, and container. A support mat having good wickingproperties for the electrolyte, such as those described herein, enablesthe mat to hold some of the electrolyte and cover the electrodes whenthe volume of the electrolyte reduces due to the exposure of hightemperatures for a prolonged period of time. As such, the oxidization ofthe negative plate can be minimized.

Conventional pasting papers typically do not reduce the porosity and/orair permeability of the pasting paper due to the increase in electricalresistance that results for a decreased porosity and/or air permeabilityof the pasting paper. For example, the average pore size of some pastingpapers is larger than 1 mm and the air perm measured by the Frazier testdescribed by ASTM Standard Method 0737 is usually over 1000 cfm/ft2 (at125 Pa). One reason that conventional pasting papers are not concernedwith decreased pore size and/or air permeability is that an average poresize that is too low significantly increases the internal/electricalresistance of the lead acid battery and, therefore, leads to adversebattery performance. For example, if the mat is too closed or dense, theelectrical resistance increases because the ions do not have a good pathto flow through the mat. Stated differently, a closed or dense matresults in the ions following a tortuous path through the mat, whichaffects the chemical reactions and increases the internal resistance ofthe battery.

The formula below may be used to evaluate the resistance of a separator.The formula is also applicable for evaluating the impact of a glass mat,such as a separator support or pasting paper. As indicated by theformula, with lower air perm/lower pore size, the electrical resistanceof the glass mat increases. Also when the pore size is very small, itmay negatively impact the crystallization of active material. Further,when the glass mat is more open, the glass mat may be more beneficialfor pasting of the active material since the active material canpenetrate through the glass mat and thereby achieve a betteradhesion/bonding between the glass mat and the plate. The resistance ofthe glass mat is a function of electrolyte resistivity (acid) inaddition to the design, pore structure, and composition of the glassmat. Resistance (R) of the electrolyte within a porous structure (Ω) maybe determined according to the formula:

R=pLτ ² /PA

Where p is equal to the resistivity of the electrolyte; L is equal tothe thickness of the glass mat; τ is equal to the tortuosity of the porepath (structure); P is equal to the porosity filled with acid (structureand composition); and A is equal to the cross-sectional area throughwhich ions flow.

Conventional pasting papers and separator support mats are thin and open(i.e., have larger pore sizes) to minimize the electrical resistance andmaximize the functionality and contact between the electrode andelectrolyte. Moreover, conventional pasting paper and/or separatorsupport mats having a combination of different sized fibers and/orhydrophilic components typically have “needle holes” due to beingmanufactured using a conventional wet-laid process. The needle holes arecommonly due to the pasting paper and/or separator support matsmirroring the surface upon which it is formed. For example, in aconventional wet-laid process, a wet mat is formed on a forming chain orbelt. The wet mat is then transported onto an application chain wherethe binder is applied. The mat is then transported onto the oven chainfor drying and curing. The wet mat mirrors the shape of the variouschains/belts, which commonly results in small holes (i.e., “pin-holes”or “needle holes”) forming in the mat. The wicking properties of suchpasting papers and support mats is reduced due to the existence of those“needle holes”. The needle holes also result in the pasting papers andsupport mats having larger pore sizes, which increases the airpermeability of the mats.

The pasting papers and/or separator support mats described herein areconfigured to have significantly reduced pore sizes and airpermeability. These pasting papers and/or separator support mats alsoexhibit excellent wickability and strength properties as describedabove. The small pore size and lower air permeability is an indicator ofhow closed or dense the mat's fibers are, which prevents shedding byminimizing the space that the active material can transition or moveinto. In one embodiment, the pore sizes and air permeability is reducedby employing an optimal combination of larger diameter glass fibers andsmaller diameter glass fibers. The larger diameter glass fibers aretypically fibers having a fiber diameter of greater than 6 μm, althougha fiber diameter of between 8 μm and 20 microns is more common, and afiber diameter of between about 10 μm and 15 microns is most common. Thesmaller diameter glass fibers or microfibers typically have a fiberdiameter of less than 5 μm, and more commonly between about 0.5 μm and 5μm, and most commonly between about 0.7 μm and 3 μm. The use of themicrofibers in the ranges claimed herein results in increased “bridging”of the fibers in the pasting paper. The term bridging as used hereindescribes tangling of and between the fibers within the resultingpasting paper mat. The increased tangling or bridging reduces theeffects of “needle holes” thereby essentially covering up the createdholes.

In other embodiments a hydrophilic filler or fillers with good acidresistance and large surface area can be added during the wet laidprocess to fill the needle holes that are formed during the wet-laidprocess. The added hydrophilic fillers significantly reduce the poresize and air permeability of the resulting mat and may make theresulting mat smoother. The wicking property of the resulting mat andthe ability to structurally support the active material (i.e., preventshedding of the active material) is therefore significantly improved.

According to one embodiment, a nonwoven fiber mat that is configured forreinforcing an electrode of a lead-acid battery (hereinafter pastingpaper) includes a plurality of first or microfiber glass fibers havingan average fiber diameter of less than 5 μm, and more commonly less than3 μm. As mentioned herein, in some embodiments the microfibers may nothave an average fiber diameter of about 1 μm. In a specific embodiment,the microfibers may have an average fiber diameter of about 0.7 μm. Thepasting paper may also include a plurality of second or coarse glassfibers having an average diameter of greater than 6 μm, and morecommonly between about 8 μm and 20 μm and most commonly between about 10μm and 15 μm. In a specific embodiment, the coarse glass fibers may havean average fiber diameter of about 13 μm. The pasting paper furtherincludes an acid resistant binder composition that binds the pluralityof microfibers and coarse glass fibers together.

The pasting paper includes between about 10% and about 50% by weight ofthe microfibers and between about 50% and 90% by weight of the coarseglass fibers. In a specific embodiment, the pasting paper includesapproximately 70% by weight of the coarse fibers and 30% by weight ofthe microfibers, excluding other materials that are applied to thepasting paper, such as the binder and/or any filler materials. Thepasting paper has an average pore size of between 1 μm and 100 μm andexhibits an air permeability of below 100 cubic feet per minute persquare foot (cfm/ft²) as measured by the Frazier test at 125 Paaccording to ASTM Standard Method D737. In some embodiments, the pastingpaper may have an average pore size of between 1 and 50 μm and/or mayexhibit an air permeability of below 10 cfm/ft² or even 1 cfm/ft² asmeasured by the Frazier test at 125 Pa according to ASTM Standard MethodD737.

The pore sizes described herein of between 1 μm and 10 μm or 100 μm issignificantly smaller than those used in conventional pasting paperswhile the air permeability of less than 1 cfm/ft², 10 cfm/ft², or 100cfm/ft² is also significantly less than those exhibited by conventionalpasting papers. For example, conventional pasting papers typically havea pore size of 1 mm or greater and exhibit an air permeability of 1000cfm/ft² or more. The lower pore size and/or air permeability of thepasting paper described herein may result in the internal electricalresistance of the battery being increased to some extent, but will alsogreatly increase the structural support that is offered by the pastingpaper (i.e., reduce shedding of the active material) while alsoexhibiting enhanced wickability and strength characteristics. Anyincrease in the electrical resistance of the pasting paper may becountered by the increased wickability of the pasting paper. Stateddifferently, the increased wicking properties of the pasting paper canhelp reduce the electrical resistance of the pasting paper and battery.

For example, in some embodiments, the pasting paper may exhibit anaverage wick height of between about 1 cm and about 5 cm after exposureto sulfuric acid having 40 wt. % H2SO4 and/or a specific gravity of 1.28for 10 minutes conducted according to method ISO8787, except thatsulfuric acid having 40 wt. % H2SO4 and/or a specific gravity of 1.28 isused in place of water. The pasting paper may also exhibit a tensilestrength of greater than 4 lbf/in. The pasting paper may also exhibitthe other wickability and/or strength properties described herein.

In some embodiments a hydrophilic filler or fillers may be added to thepasting paper. For example, the pasting paper may include between 0.1%and about 20% by weight of a powder or granular filler.

The powder or granular filler is hydrophilic and acid resistant and hasa surface area of greater than 10 m²/g, and in main embodiments has asurface area of 150 m²/g or greater. These powder or granular fillerdecreases the pore size and air permeability of the nonwoven fiberreinforcement mat. In some embodiments, the powder or granular filler isapplied to a second binder that is subsequently applied to the pastingpaper, commonly before the pasting paper is dried such as by adding thesecond binder simultaneously with, or close to, the application of theprimary binder. In yet other embodiments, the powder or granular fillermay be added to the primary binder or to the white water solution thatincludes the coarse and microfibers. The application of the powder orgranular filler to a binder (i.e., primary or secondary) helps bond oradhere the powered filler to the pasting paper after application of thefiller.

The powder or granular filler may comprises about 20% or less by weightof the primary or second binder composition that is applied to thenonwoven fiber reinforcement mat. The amount of powder or granularfiller that is included in the binder may depend on the machine that isused to mix and/or apply the binder. The amount of 20% may be an upperlimit for high end mixing and/or application machines while an amount ofless than 10% by weight of the filler material may be more common. Anamount of between 2% or 4% of the powered filler may be more ideal forapplication to the pasting papers since these amounts are easier to mix,control, and/or apply to the pasting paper. For example, in someinstances the use of more than 4% of the powder or granular filler byweight of the binder may negatively affect removal of the binder and/orother aqueous solutions. The application of too much powder or granularfiller can essentially create an impermeable or nearly impermeablesurface that decreases the amount of water or other liquids that may bevacuumed out of the pasting paper, thereby negatively affecting dryingof the pasting paper. As such, an application of less than 10% by weightof the powder or granular filler may be preferred with an application ofless than 5% by weight, such as 2% to 4%, being most preferred.

Due to the decreased pore size and air permeability of the pastingpapers described herein, the papers function as filters that filter outthe powder or granular filler from the applied binder. As such, theresulting amount of powder or granular filler in the pasting paper istypically greater than the amount that is used in the binder. Stateddifferently, because the pasting paper filters the powder or granularfiller out of the applied binder, the concentration of the powder orgranular filler in the pasting paper may be greater than theconcentration of powder or granular filler in the binder. Theconcentration of the powder or granular filler in the pasting paperdepends on the amount of time that the binder/powder or granular filleris applied to the pasting paper with longer applications resulting in agreater concentration and shorter applications resulting in a lesserconcentration. Regardless of the concentration of the powder or granularfiller in the binder, the binder may be applied to the pasting paper toachieve a concentration of between 0.1% and 20% by weight of the powderor granular filler in the pasting paper as described herein.

In some embodiments, the powder or granular filler may be a silicamaterial, such as synthetic precipitated silica, SiC, silicon carbide,and the like. An example of synthetic precipitated silica that may beused with the embodiments described herein is Hi-Sil™ 233-D, 233G-D,and/or WB-37 manufactured by PPG Industries, Inc. Other appropriateinorganic fillers can also be used and/or more than one filler may beused. Synthetic precipitated silica is an extremely hydrophilicmaterial. As such, in addition to decreasing the pore size and airpermeability of the pasting paper via filling of the holes in thepasting paper, the use of the synthetic precipitated silica greatlyincreases the wickability of the pasting paper. The use of the syntheticprecipitated silica also enables a greater portion of coarse glassfibers to be used (e.g., having a fiber diameter greater than 6 μm andnormally between 8 μm and 20 μm), thereby greatly increasing thestrength of the pasting paper without significantly affecting anddecreasing the wickability. Other materials, like wetting agents, canalso be added to further improve the wicking property of the mat.

Referring now to FIG. 5, illustrated is a method 500 of making anonwoven fiber mat for use in reinforcing an electrode of a lead-acidbattery, or supporting a separator of a lead-acid battery. At block 502,a plurality of first glass fibers is mixed with a plurality of secondglass fibers in a white water solution. The plurality of first glassfibers have an average fiber diameter of less than 5 μm, and commonlyless than 3 μm. In a specific embodiment, the first glass fibers have anaverage fiber diameter of about 0.7 μm. The plurality of second glassfibers have an average fiber diameter of greater than 6 μm, and morecommonly have a fiber diameter between about 8 μm and 20 μm, and morecommonly between about 10 μm and 15 μm. In a specific embodiment, thesecond glass fibers have an average fiber diameter of about 13 μm.

At block 504, a liquid of the white water solution is removed to form awet laid mat that includes about 10% and about 50% by weight of theplurality of first glass fibers and between about 50% and 90% by weightof the plurality of second glass fibers. The liquid is typically removedby positioning the white water solution on an a porous or semi-porousconveyor and applying a vacuum to the white water solution. At block506, a binder composition is added to the wet laid mat. At block 508,the wet laid mat and binder composition are dried to form the nonwovenfiber mat. The nonwoven fiber mat is formed to have an average pore sizeof between 1 μm and 100 μm and exhibit an air permeability of below 100cubic feet per minute per square foot (cfm/ft²) as measured by theFrazier test at 125 Pa according to ASTM Standard Method D737. Asdescribed herein, the nonwoven fiber mat may be formed to have an evensmaller average pore size (e.g., between 1 μm and 10 μm) and/or exhibitan even lower air permeability (e.g., less than 10 cfm/ft² or less than1 cfm/ft²).

In some embodiments, between 0.1% and about 20% by weight of a powder orgranular filler is added to the nonwoven fiber mat. The powder orgranular filler is hydrophilic and acid resistant and has a surface areaof greater than 10 m²/g, and in many embodiments has a surface area of150 m²/g or greater. In such embodiments, the powder or granular fillermay be applied to the binder that is applied to the wet-laid mat atblock 506. In other embodiments, the powder or granular filler may beadded to the white water solution with the first and second glassfibers. In still other embodiments, the powder or granular filler may beadded to a secondary binder that is applied to the nonwoven fiber mat.In such embodiments, the powder or granular filler may comprises lessthan 20% by weight of the secondary binder composition, although in manyembodiments, the powder or granular filler comprises between 1% and 4%by weight of the secondary binder composition. The secondary bindercomposition may be applied to the nonwoven fiber mat after drying of thewet laid mat and binder composition. In some embodiments, application ofthe powder or granular filler may be achieved via a combination of anyof the above described application processes. The powder or granularfiller may include a synthetic precipitated silica.

The above described nonwoven fiber mat having low air permeability andsmall pore sizes may be especially useful as a pasting paper thatreinforces and structurally supports electrodes of lead-acid batteries.The small pore sizes of the nonwoven fiber mats creates a closed up andmore impermeable mat that is well suited to reduce shedding of theelectrode's active material. These mats may be less suited for use instructurally supporting polymeric film separators due to the small poresizes and the negative effects that the more impermeable mats may haveon the transport of ions and/or the electrolyte, although the negativeeffects of the mats may be reduced or countered due to the increase inwickability (e.g., resistance may be reduced as the mat is wetted by theelectrolyte). For example, separator support mats are typically thin andopen to minimize electrical resistance and maximize ion transport andthe associated chemical reactions. For example, the pasting paper matsdescribed here are normally between 5 and 50 mils thick.

Referring now to FIG. 6, illustrated is a method 600 of making anon-woven fiber mat. Method 600 may include mixing a first plurality offirst glass fibers and a second plurality of second glass fibers to forma mixture of glass fibers 602. The first plurality of first glass fibersmay have diameters of less than 5 μm, between about 0.5 μm and about 1.0μm, or about 0.7 μm, for example. The second plurality of second glassfibers may have diameters of greater than 6 μm. For example, the secondglass fibers may have diameters of between about 8 μm and about 13 μm,between about 8 μm and about 10 μm, or between about 11 μm and 13 μm.The first plurality of first glass fibers may have a weight betweenabout 10% and about 50%, between about 30% in about 40%, or betweenabout 15% and about 30% of the combined weight of the first plurality offirst glass fibers and the second plurality of second glass fibers.While conventional nonwoven fiber mats for batteries may include moremicrofibers than coarse fiber, methods described herein with more coarsefiber than microfiber may produce a nonwoven fiber mat with increasedmechanical strength. The mat's increased mechanical strength may resultin a decreased, though still sufficient, wickability.

The first glass fibers may include a first glass composition, and thesecond glass fibers may include a second glass composition, where thefirst glass composition is different from the second glass composition.For example, different glass compositions include compositions withalumina (Al2O3), sodium oxide (Na2O), potassium oxide (K2O), boric oxide(B2O3), calcium oxide (CaO), magnesium oxide (MgO), or other compounds.

Method 600 may also include adding a binder composition to the mixtureof glass fibers to form a slurry 604. The method may further includemaintaining a pH of the slurry at about 7 or higher. The pH of theslurry may be non-acidic or from neutral to slightly basic. For example,the pH of the slurry may be maintained between about 7 and about 8.5.Without a high concentration of smaller diameter fibers, acid or acidicconditions may not be needed to increase the dispersion of these smallerdiameter fibers. Reducing or eliminating the acid needed may holdprocessing advantages.

The method may include adding a powder or granular filler to the mixtureof glass fibers. The powder or granular filler may increase wickability,possibly to counteract the decreased wickability with the decreasedconcentration of microfibers. The powder or granular filler may behydrophilic and acid-resistant. For example, the powder or granularfiller may be silica or synthetic precipitated silica. The powder orgranular filler may between about 0.1% and about 10% by weight of thenonwoven fiber mat. The coarse fibers and the microfibers together mayhelp hold the powder or granular filler in the mixture or slurry orfinished nonwoven fiber mat.

The method may further include forming a mat, drying the mat, and curingthe mat. Drying the mat may include blowing air through the mixture ofglass fibers. A through-air dryer may dry the mixture of glass fibersand the cured binder composition. Method 600 may exclude drum dryers.Drum dryers may dry conventional nonwoven fiber mats by direct orsubstantially direct contact. In contrast, because of lowerconcentrations of microfibers in these and other methods, air may passthrough the nonwoven fiber mat and dry the mat. Sufficient air to drythe mat may not be able to pass through a conventional nonwoven fibermat.

The mixing, adding, drying operations in methods may be continuousprocesses. These operations may not be batch or semi-batch processes. Inother words, these operations may be run continuously and withoutinterruption. Continuous operation may allow for a faster throughput andmore cost effective operation.

These or other examples of the present technology may include alead-acid battery. The battery may include a positive electrode, anegative electrode, and a nonwoven fiber mat disposed adjacent positiveelectrode or the negative electrode. The nonwoven fiber mat include afirst plurality of first glass fibers having diameters of less than 5μm. The nonwoven fiber mat may further include a second plurality ofsecond glass fibers having diameters greater than 6 μm. The firstplurality of first glass fibers may make up between about 10% and about50% by weight of the combined weight of the first plurality of firstglass fibers and the second plurality of second glass fibers. Thenonwoven fiber mat may also include a binder composition. The nonwovenfiber mat may have an average wick height of between about 1 cm andabout 5 cm after exposure to sulfuric acid having 40 wt. % H2SO4 and/ora specific gravity of 1.28 for 10 minutes conducted according to methodISO8787 except that sulfuric acid having 40 wt. % H2SO4 and/or aspecific gravity of 1.28 is used in place of water. The nonwoven fibermat may also have a total tensile strength of greater than 4 lbf/in. Thenonwoven fiber mat may be any nonwoven fiber mat described herein. Thelead-acid battery may further include a filler. The filler may besynthetic precipitated silica or any filler described herein.

EXAMPLES Example 1

Nonwoven glass mat samples were made with a pilot wet-laid machine.Process water with pH greater than 5 was used. The following JohnsManville glass fibers were used: K249T with a nominal fiber diameter ofabout 13 μm and a length of % inch; 206-253 with a nominal fiberdiameter of about 0.765 μm; 210X-253 with a nominal fiber diameter ofabout 3.0 μm; and 8 μm/8 mm C glass with a nominal fiber diameter ofabout 8 μm and a length of 8 mm. The compositions of the nonwoven fibermats are shown in Table 1.

Air permeability was measured by the Frazier test, which is described byASTM Standard Method D737. This test was usually carried out at adifferential pressure of about 0.5 inches of water. Wicking strength perlength or capillary rise was determined by ISO8787, with the wickingmedium being 40 wt. % sulfuric acid. Thickness was measured with a gaugeunder pressure of 1.868 kPa or 10 kPa. Tensile strength of a 1 inch widesample was measured using an ASTM method by an Instron machine. Tensilestrength was measured in the machine direction (MD) and thecross-machine direction (CMD). The performance of the nonwoven fibermats is shown in Table 2.

TABLE 1 Nonwoven fiber mat properties Sample Mat Weight Micro- Micro- ID(lb/sq) LOI fiber % Coarse Fiber fiber A 0.7 10% 50 K249T 206-253 B 0.720% 50 K249T 206-253 C 0.7  5% 40 K249T 206-253 D 0.7 10% 40 K249T206-253 E 0.7 20% 40 K249T 206-253 F 0.7 10% 30 K249T 206-253 G 0.7 20%30 K249T 206-253 H 0.5  5% 40 K249T 206-253 I 0.5 10% 40 K249T 206-253 J0.5 20% 40 K249T 206-253 K 0.5 10% 30 K249T 206-253 L 0.5 20% 30 K249T206-253 M 0.7 10% 50 8 um/8 mmC 210X-253  N 0.7 10% 80 8 um/8 mmC210X-253  O 0.7 10% 50 K249T 210X-253  P 0.7 10% 80 K249T 210X-253 

TABLE 2 Nonwoven glass mat performance characteristics Total Ave. Ave.tensile Ave. Ave. Wicking Wicking strength Ave. Thickness ThicknessLength Length Ave. Ave. normalized Air under under at at MD CMD byweight Sample Perm 1.686 kPa 10 kPa 10 min. 1 hr Tensile Tensile[(lbf/in)/ ID (cfm/ft²) (mil) (mil) (cm) (cm) (lbf/in) (lbf/in) (lb/sq)]A 69.7 13.8 5.0 2.3 4.55 0.73 0.85 2.26 B 63.4 17.3 6.3 1.55 3.65 2.032.7 6.76 C 60.2 13.75 4.9 2.0 4.2 0.33 0.3 0.90 D 115 13.95 5.6 1.6 3.151.1 1.25 3.36 E 116.7 14.85 6.1 0.8 1.95 2.53 2.82 7.64 F 144.1 13.7 6.11.2 2.65 1.86 2.36 6.03 G 208.5 13.5 7.0 0.3 0.8 5.2 5.18 14.8 H 131.811.2 4.0 0.9 2.9 0.19 0.22 0.82 I 171.5 11.75 4.2 0.45 1.25 1.0 1.334.66 J 304.3 11.05 4.0 0.3 1.5 2.2 3.8 12 K 325.7 10.35 4.1 0.2 0.451.31 1.85 6.32 L 435.6 9.55 4.5 0.5 1.0 2.73 4.27 14 M 398.5 10.1 3.90.3 0.7 0.57 0.48 1.50 N 350.0 12.15 4.5 0.35 0.55 0.58 0.55 1.61 O567.8 12.9 5.2 0.3 0.55 1.27 2.33 5.14 P 382.3 14.15 5.0 0.4 0.55 0.620.98 2.29

When the percentage of microfiber increases from 30% to 50%, especiallyfor microfiber 206-253, the processing difficulty increases. A nonwovenglass mat with 206-253 at 50% and LOI at 10% is challenging to processbecause of lower strength. As example 1 illustrates, when the percentageof microfibers is increased, the wickability of the mat is improved andthe air permeability and strength are reduced. As shown in some of thelater examples (e.g., Example 4), adding a powder filler to the mat(e.g., silica) improves the mat's wickability without compromising themat's strength. Additional trials have shown that the addition of silicadid not compromise the strength of the mat. It is believed that the maincontribution for the mat's strength is from the binder and thepercentage of coarse fibers.

Example 2

Nonwoven glass mat samples were made with a commercial wet-laid machine.Process water with pH greater than 5 was used. The following JohnsManville glass fibers were used: K249T with a nominal fiber diameter ofabout 13 μm and a length of ¾ inch; and 206-253 with a nominal fiberdiameter of about 0.765 μm.

Air permeability was measured by the TEXTEST™ FX 3300 according to ASTMStandard Method D737. This test was usually carried out at adifferential pressure of about 0.5 inches of water. Wicking strength perlength or capillary rise was determined by ISO8787, with the wickingmedium being 40 wt. % sulfuric acid. Thickness was measured with a gaugeunder pressure of 10 kPa. Tensile strength of a 3 inch wide sample wasmeasured using an ASTM method by an Instron machine.

Table 3 shows the compositions of nonwoven fiber mats along withresults. Total tensile strength is normalized by the weight of the mat.The non-dimensionalized tensile strength is significantly higher forsamples in this example than in Example 1. Example 2 illustrates trendsthat are similar to those illustrated in Example 1. Specifically, thatwhen the percentage of microfibers is increased, the wickability of themat is improved and the air permeability and strength are reduced.

TABLE 3 Nonwoven fiber mat properties Total tensile strength Wickingnormalized K249T/ Base Air MD CD length @ Thickness by weight 206-253LOI wt. perm Tensile Tensile 1 hr (mil) @ [(lbf/in)/ ratio (%) (lb/sq)(cfm) (lb/3″) (lb/3″) (cm) 10 kPa (lb/sq)] 90/10 26.4 1.17 300 80 46 0.911 108 80/20 18.7 1.14 183 45.4 25.9 3.5 9.7 63 80/20 14.7 1.16 176 39.417.5 3.9 8.9 49 80/20 19.5 1.18 158 53.1 26.5 4.4 9.5 67 75/25 17.6 1.12101 43.6 16 4.6 7.6 53 75/25 18.1 1.21 105 47 18.9 4.9 9.7 54 75/25 19.81.14 114 45.3 20.4 4.8 8.4 58

Example 3

Samples were measured for their Cobb₆₀ degree as an indication of theirhydrophilic or wickability properties. The following Johns Manvilleglass fibers were used: K249T with a nominal fiber diameter of about 13μm and a length of % inch; and 206-253 with a nominal fiber diameter ofabout 0.765 μm. In these experiments, a 1.1 lb/sq mat with 75% K249T and25% 206-253 with 20% LOI were used. Both sides of samples—the binderrich side and the wire side—were measured. The results are shown inTables 4 and 5.

TABLE 4 Binder-rich side Cobb₆₀ degree Absorded Absorded Absorded amount(g Sample amount (g) amount (g/m²) water/g mat) 1 0.42 42 0.78 2 0.45 450.84 3 0.38 38 0.71 4 0.37 37 0.69 5 0.37 37 0.69 6 0.35 35 0.65 7 0.3737 0.69 Average 0.39 38.71 0.72 Std. Dev. 0.03 3.50 0.07

TABLE 5 Wire side Cobb₆₀ degree Absorded Absorded Absorded amount (gSample amount (g) amount (g/m²) water/g mat) 1 0.43 43 0.80 2 0.47 470.88 3 0.41 41 0.76 4 0.41 41 0.76 5 0.45 45 0.84 6 0.45 45 0.84 7 0.3939 0.73 Average 0.43 43.00 0.80 Std. Dev. 0.03 2.83 0.05

As illustrated in Example 3, with all samples tested, the Cobb60 degreeis less than 1. This means that the sample adsorbs a weight of waterless than or equal to the weight of the mat. However, with the additionof silica, the Cobb60 value may be larger than 1.

Example 4

A series of nonwoven glass mat samples were made with a pilot wet-laidmachine. A typical process water with pH>5 was used. The nonwoven glassmat samples included 13 μm and ¾″ T glass fibers (K249) and 0.765 μm206-253 microglass fibers that are both manufactured by Johns Manville.The glass fibers were blended at a ratio of 70/30 with 70% T glassfibers and 30% 206-253 microglass fibers. A silica filler (Hi-Sil™ 233)was added to the binder solution at ratios to the binder solids of 2%and 4% respectively. RHOPLEX™ HA-16 from Dow Chemical Company was usedas the binder. A control sample mat was constructed having the samefiber configuration as the other mats, but without having silica added.As shown in Table 6 below, the addition of silica significantly closedup the mat and therefore reduced the air permeability values. Becausethe “holes” in the mat were filled by silica, the mat was more uniformand the wicking strength was dramatically improved.

TABLE 6 nonwoven fibers mats with added silica K249T/ Wt. % Wickinglength 206-253 LOI Base wt. of silica Air perm @10 mins ratio (%)(lb/sq) in the mat (cfm) (cm) 70/30 20.3 1.11 0 77 1.1 70/30 23 1.4512.7 11 4.4 70/30 25.9 1.16 15.3 3.2 4.3

The air permeability of the nonwoven mats was measured by the Fraziertest described by ASTM Standard Method D737, with the results given inunits of cubic feet per minute per square foot (cfm/ft²). The test wascarried out at a differential pressure of about 0.5 inches of water. Themeasured wicking strength/length, or capillary rise, is defined inISO8787, however, the wicking medium was 40 wt. % sulfuric acid insteadof water. As can be seen from Table 6, the addition of the silicaincreased the base weight of the mat. The binder content, as measured byLoss on Ignition, was relatively the same between the three mats.However, the air permeability significantly decreased while thewickability significantly increased for the samples with added silica.Accordingly, the addition of powder or granular silica significantly“closed up” the mat thereby enabling the mat to limit shedding of theactive material as described herein while providing excellentwickability properties.

In the preceding description, for the purposes of explanation, numerousdetails have been set forth in order to provide an understanding ofvarious examples of the present technology. It will be apparent to oneskilled in the art, however, that certain examples may be practicedwithout some of these details, or with additional details.

Having described several examples, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Additionally, details of any specific example may notalways be present in variations of that example or may be added to otherexamples.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neither,or both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a method” includes aplurality of such methods and reference to “the glass fiber” includesreference to one or more glass fibers and equivalents thereof known tothose skilled in the art, and so forth. The invention has now beendescribed in detail for the purposes of clarity and understanding.However, it will be appreciated that certain changes and modificationsmay be practice within the scope of the appended claims.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A method of making a nonwoven fiber mat for usein reinforcing an electrode of a lead-acid battery, the methodcomprising: mixing a plurality of first glass fibers with a plurality ofsecond glass fibers in a white water solution, wherein: the plurality offirst glass fibers have an average fiber diameter of less than 5 μm; andthe plurality of second glass fibers have an average fiber diameter ofgreater than 6 μm removing a liquid of the white water solution to forma wet laid mat comprising about 10% and about 50% by weight of theplurality of first glass fibers and between about 50% and 90% by weightof the plurality of second glass fibers; adding a binder composition tothe wet laid mat; and drying the wet laid mat and binder composition toproduce the nonwoven fiber mat such that the nonwoven fiber mat has anaverage pore size of between 1 μm and 100 μm and exhibits an airpermeability of below 100 cubic feet per minute per square foot(cfm/ft²) as measured by the Frazier test at 125 Pa according to ASTMStandard Method D737.
 2. The method of claim 1, further comprisingapplying between 0.1% and about 20% by weight of a powder or granularfiller to the nonwoven fiber mat, wherein the powder or granular filleris hydrophilic and acid resistant and has a surface area of greater than10 m²/g.
 3. The method of claim 2, wherein the powder or granular filleris added to the white water solution or the binder composition.
 4. Themethod of claim 2, wherein the powder or granular filler comprisessynthetic precipitated silica.
 5. The method of claim 2, wherein thenonwoven fiber mat exhibits an air permeability of below 10 cfm/ft² asmeasured by the Frazier test at 125 Pa according to ASTM Standard MethodD737.
 6. The method of claim 1, wherein the plurality of first glassfibers have an average fiber diameter of about 0.7 μm.
 7. The method ofclaim 1, wherein nonwoven fiber mat exhibits: an average wick height ofbetween about 1 cm and about 5 cm after exposure to sulfuric acid having40 wt. % H2SO4 or a specific gravity of 1.28 for 10 minutes conductedaccording to method ISO8787, and a total normalized tensile strength ofgreater than 4 lbf/in.
 8. The method of claim 1, wherein the nonwovenfiber mat has an average pore size of between 1 and 10 μm.
 9. The methodof claim 1, wherein the nonwoven fiber mat exhibits an air permeabilityof below 10 cfm/ft² as measured by the Frazier test at 125 Pa accordingto ASTM Standard Method D737.
 10. The method of claim 9, wherein thenonwoven fiber mat exhibits an air permeability of below 1 cfm/ft² asmeasured by the Frazier test at 125 Pa according to ASTM Standard MethodD737.
 11. A method of reinforcing an electrode of a lead-acid batterywith a nonwoven fiber mat, the method comprising: mixing a plurality offirst glass fibers with a plurality of second glass fibers in a whitewater solution, wherein: the plurality of first glass fibers have anaverage fiber diameter of less than 5 μm; and the plurality of secondglass fibers have an average fiber diameter of greater than 6 μmremoving a liquid of the white water solution to form a wet laid matcomprising about 10% and about 50% by weight of the plurality of firstglass fibers and between about 50% and 90% by weight of the plurality ofsecond glass fibers; adding a binder composition to the wet laid mat;drying the wet laid mat and binder composition to produce the nonwovenfiber mat such that the nonwoven fiber mat has an average pore size ofbetween 1 μm and 100 μm and exhibits an air permeability of below 100cubic feet per minute per square foot (cfm/ft²) as measured by theFrazier test at 125 Pa according to ASTM Standard Method D737; andpositioning the nonwoven fiber mat adjacent the electrode to reinforcethe electrode.
 12. The method of claim 11, further comprising applyingbetween 0.1% and about 20% by weight of a powder or granular filler tothe nonwoven fiber mat, wherein the powder or granular filler ishydrophilic and acid resistant and has a surface area of greater than 10m²/g.
 13. The method of claim 12, wherein the powder or granular filleris added to the white water solution or the binder composition.
 14. Themethod of claim 12, wherein the powder or granular filler comprisessynthetic precipitated silica.
 15. The method of claim 11, wherein thenonwoven fiber mat has an average pore size of between 1 and 10 μm. 16.The method of claim 11, wherein the nonwoven fiber mat exhibits an airpermeability of below 10 cfm/ft² as measured by the Frazier test at 125Pa according to ASTM Standard Method D737.
 17. The method of claim 11,wherein the nonwoven fiber mat exhibits an air permeability of below 1cfm/ft² as measured by the Frazier test at 125 Pa according to ASTMStandard Method D737.
 18. The method of claim 11, wherein nonwoven fibermat exhibits: an average wick height of between about 1 cm and about 5cm after exposure to sulfuric acid having 40 wt. % H2SO4 or a specificgravity of 1.28 for 10 minutes conducted according to method ISO8787,and a tensile strength of greater than 4 lbf/in.
 19. The method of claim11, wherein the plurality of first glass fibers have an average fiberdiameter of about 0.7 μm.